Similarly, in I3D [1]}, a stack of RGB and optical flow frames from each snippet \(s_n\)  are fed to I3D network, extracting spatial and temporal feature vectors \(f_{S, n}\)  and \(f_{T, n}\)  which are concatenated to create feature \(f_n\) . In C3D [2]}, the frames of each snippet \(s_n\)  are directly fed to a 3D-CNN architecture to capture spatio-temporal information, and extracting feature vector \(f_n\) .
